In the past, there have been proposed various kinds of DC switches located in a power supply line between a DC power source and a DC load.
This kind of DC switch includes a housing provided with a power connection terminal to be connected to a power source and a load connection terminal to be connected to a load. Moreover, the DC switch includes mechanical contacts interposed between the power connection terminal and the load connection terminal. The mechanical contacts include a stationary contact and a movable contact capable of moving to contact the stationary contact and to separate from the stationary contact. The DC switch further includes a switching mechanism unit having an operating handle used for manual operation and movably attached to the housing, and the switching mechanism unit is configured to open and close the mechanical contacts in response to the manual operation of the operating handle.
In the aforementioned DC switch, to move the operating handle between an open position (position where the mechanical contacts are opened) and a close position (position where the mechanical contacts are closed) is capable of turning on and off the mechanical contacts.
At an instance of that the mechanical contacts are turned off, a potential difference between the stationary contact and movable contact is likely to cause an arc (arc discharge). Such an arc discharge may cause welding the movable contact and the stationary contact and damaging each of the stationary contact and movable contact.
Especially, in the case of the DC switch, since current flowing through the mechanical contacts is a DC current, the current flowing through the mechanical contacts has no zero point (zero crossover point) differently from an AC current. Therefore, once the arc occurs, the arc is not easily extinguished, and is likely to be maintained for a long time. Moreover, because of that a current flows only in one direction in contrast to an AC current, it is likely to see a contact shift where one of the contacts is melted and flown to the other of the contacts. Therefore, a defect where contacts can not separate from each other is likely to occur.
Consequently, there has been proposed a DC switch which is capable of extinguishing an occurred arc immediately (see Japanese Non-examined Patent Publication No. 10-154448, for example). The DC switch disclosed in the aforementioned Japanese Non-examined Patent Publication includes an extinguishing device which extinguishes an arc across contacts by elongating it by use of a Lorentz force.
Although the DC switch disclosed in the aforementioned Japanese Non-examined Patent Publication includes the extinguishing device capable of immediately extinguishing an occurred arc, the arc can occur. Therefore, it is not enough to prevent the contact shift and a contact welding caused by the arc.